Aside from a car or a whack of cash, a great memory is the best graduation gift I can think of. I don't know about you but that car and cash thing just aren't happening, so the video slideshow might be right up your alley.
Although it may seem like a quick and easy thing to do, and it can be if you aren't putting in any actual effort to make it personal, a thoughtful, memorable video slideshow can take a lot of time to prepare for and create. If you are going this route, I suggest giving yourself at least two months, depending on how much time you have to commit to it.
The first three weeks can be dedicated to locating and gathering the perfect pictures and deciding the theme for the project. Will it only include school photos or their life up to this point? Will you use just photos or will their be memorabilia and videos as well? Flipping through albums, boxes and our often disorganized digital image collections can take time. Especially if you get misty eyed reliving events as you go. Have a criteria for the types of pictures you are looking for to keep you on task. You may want to contact your graduate's friends for additional social media images to add in.
The next three weeks will likely involve digitizing the prints and memorabilia, editing any videos into usable clips setting up a storyboard with the order of the images as you want them to appear. To make it thoughtful and memorable, you want to tell their story not just a bunch of random images. Think about how you want to separate the parts of the story into chapters and add any captions you think may enhance the story. Don't go overboard with the captions, people don't want to have to read every slide.
The last couple of weeks will be uploading into your chosen software, editing the appropriate slide lengths and transitions and choosing and adding the music, fades and timing. Remember that you will need to check into copyrights for images and music if you intend to show it outside of your event or home. You don't want to violate copyright if its going on-line. I use Proshow Pro software but there are many excellent options available out there.
If you find this overwhelming, simply collect your images and videos and find someone local to do the work for you. Just be sure to give them the necessary time to do a great job on it as well. Your slideshow will likely be something they will remember and watch over and over again over the years, so all the work will be worth it.